Heat a 12-inch cast iron frying pan over medium heat. Fry the pancetta, turning it frequently so that it browns and crisps on all sides; this takes about 10 minutes. Remove it with a slotted spoon and drain it on paper towels. Leave the heat on and the renderings in the pan. (With a well-seasoned cast iron, this should be all the fat you need to cook the remainder of the hash. If you’re not using a cast iron, you might need to add a tablespoon or so of oil; if you’ve skipped the pork, you’ll want to start with 2 tablespoons oil.)

Add the potatoes don’t move them for a couple minutes. Use this time to season them well with salt and pepper. Once they’ve gotten a little brown underneath, begin flipping and turning them, then letting them cook again for a few minutes. The idea is not to fight them off the frying pan, once they’ve gotten a little color, it’s easier to flip them and you’ve gotten closer to your goal of getting them evenly browned.

When the potatoes are about three-fourths as crisped and brown as you’d like them — this takes about 15 minutes — add the onion. (I add this now, not earlier, because I find it often burns before the potatoes are done.) Cook for an additional 5 minutes. Add the asparagus, cover the pan and cook for 5 to 8 minutes, or until crisply cooked. (Skinny asparagus will take just 5 minutes; thicker asparagus will take longer.) Remove the lid, return the pancetta to the pan for another minute, to reheat. Taste for seasoning and adjust if needed. Serve immediately.